Probably some data is missing, as following can indicate. "BPD", "ptb" quantities are supposed at some "standard" temperature.
1. Crude in : 60000 BPD (blue figures are given quantities).
Water in: 60000x5% = 3000 BPD
Water effluent (brine): 6667 BPD
Crude out : 60000+3000-6667 = 56333 BPD (assumed same as "crude oil effluent").
2. Salt with crude in : 60x4000 = 240000 lb/d (ptb=pounds per thousand barrels).
Salt with water in : 4x400 = 1600 lb/d
Total salt in : 240000+1600 = 241600 lb/d
Assumed salt content in brine out: 33000 ptb, figure missing (red figures arbitrarily supposed for an example).
Salt with brine out : 6.667x33000 = 220011 lb/d
Salt with crude out : 241600 - 220011 = 21589 lb/d (*)
Extent of salt removal from crude: 1-21589/240000 = 0.91, or 91%
3.1 "Desalting of Crude oil" can be seen in Nelson, Petroleum Refinery Engineering, McGraw-Hill, 1958), pages 265-268.
3.2 One could measure another quantity (e.g. salt content of crude out) instead of salt content of brine.
3.3 (*) Water content of 0.2% in crude out would mean 56333x0.2%=112.7 BPD of water. Assuming all diluted salt is in water, its salt content would be ~190000 ptb, which is unrealistically high (expected around 33000 ptb). Or probably 0.2% water is too low.
On the other hand usual salt removal efficiency is ~ 90% (per 3.1). If the data is experimental, new measurement with additional data has to be realized, to clarify the balance.
3.4 Salt content of 35636 ptb in brine would result in "salt with crude out" 241600-6.667x35636 = 4015 lb/d, and salt content 4015/0.1127 = 35625 ~ 35636 ptb in the water of crude out. This could close the salt balance in theory, but salt removal efficiency from crude would be (240000-4015)/240000 = 98.3 % , which seems too high.
3.5 Comments on all above text are welcomed. Desalter brine met in local refinery had salt content ~1.5 g/l = 526 ptb, differing to present picture.
Edited by kkala, 25 February 2013 - 06:35 PM.